a) Field of the Invention
The present invention relates to a refraction-type LED (Light Emitting Diode) ceiling lamp, and more particularly to a plate-type ceiling lamp which is used on an indoor ceiling with a limited projection angle to project brilliance on a limited area on a ground, forming uniform light beams of emission and effectively defining a projection area. In addition, the ceiling lamp can be assembled on the ceiling successfully and can be cooled spontaneously.
b) Description of the Prior Art
In a wave of saving energy and reducing carbon dioxide emission, energy-saving illumination equipment has become a mainstream in household or office illumination. A fluorescent light and an LED lamp can save energy, yet as an existing LED lamp is deployed as a dot-matrix distribution, the LED lamp is a point source of light in the dot-shape distribution if viewing from outside. In addition, due to an error in a manufacturing process or of a material, each LED lamp will have a different illumination efficiency and wavelength, and a color render index of the LED lamp will be inferior. Whereas, a conventional fluorescent light is provided with uniform brightness, and the color render index and intensity of illumination are uniform and soft by a new three-wavelength technology. Therefore, for an implementation using the LED as an illumination element, light beams should be transformed through an optical mechanism so as to be applied to indoor illumination.
In general, a quantity of illumination devices is determined by a floor space size in a room. For example, an office of about 6-8 m2 (meter) will require 100 W (watt) of illumination equipment for reading and an illumination angle should be less than 180° in principle, whereas the illumination angle is set at 180° for the illumination equipment that is provided with a directionality function so as to define a specific illumination angle for an illumination area. Although utilization of light energy can be satisfied through defining the illumination angle to prevent from unnecessary loading to the light energy, it is difficult to define the illumination angle for an ordinary lamp-set.
An LED illumination business has been recognized as one of the promising businesses in recent years, mainly due to a small size and light weight. If the LED can be applied to illumination, a household space will be provided with a more flexible utilization mode and an effect of energy-saving can be expected. The LED is small in size and has a fast response time, and does not have a danger of mercury in the conventional fluorescent light; these are all the advantages of the LED. However, the LED that is applied in the household illumination should operate at a high power; hence, waste heat will be generated correspondingly. In addition, a working temperature of an LED lamp-set system cannot be too high and a total temperature difference should not be higher than 15° to prevent from thermal strain degradation of material by heat or prevent the material from undergoing a vicious cycle by a resistance factor that the efficiency is lost. If the lost of efficiency exceeds 10%, then the brilliance of projection will decrease explicitly, which largely reduces a total lumen of light flux at the projection area.
An existing LED illumination design includes U.S. Pat. No. 6,540,373 B2 disclosing a slab on which multiple LED excitation units are arranged in a matrix. The slab is one of the plates forming a ceiling and therefore, light can be emitted downward. However, as the excitation unit is a point source of light, appearance will offend eyes and lumen or a color temperature will be non-uniform due to the manufacturing error.
In U.S. Pat. No. 6,355,961 B1, a projection surface of the LEDs, arranged in a matrix, is provided with a photo-rectifier to dissipate light spots, and in another U.S. Pat. No. 7,311,423 B2, a location where a conventional fluorescent light resides is replaced with an LED, having a same issue of an explicit point source of light.
In terms of a light beam modulation technology, there is US Publication No. 2001/0046131 A1 wherein a mixing chamber is utilized to reflect a light beam operation part, with the light beam being pre-expanded through a diffuser assembly and then entering into a light guide plate. In addition, a direction of the light beam is changed at a reflection surface to serve as backlit for an LED board. This invention is utilized in a different situation and the methods of pre-mixing and pre-diffusing are employed. Therefore, a light flux has been lost significantly before entering into the light guide plate in spite that when the light beam is used for the LED backlit, the brightness is very uniform. Nevertheless, for the indoor illumination that focuses on the energy saving, the loss from the light beam pre-transformation operation does not facilitate a general implementation.